Biocompatible titanium base alloys are described in a number of United States patents including the following:
______________________________________ Steinemann et al 4,040,129 issued August 09, 1973 Wang et al 4,857,269 issued August 18, 1989 Wang et al 4,952,236 issued August 28, 1990 and Davidson et al 5,169,597 issued December 02, 1992. ______________________________________
The disclosures of these patents are incorporated in this application as representing the state of the art to which this invention relates and for their descriptions of such prior art.
The present invention is an improvement over the alloys described in the above noted patents insofar as it provides novel fully biocompatible alloys with a low modulus of elasticity.
In the Steinemann et al patent the toxicity of various elements are discussed and alloys of titanium and/or zirconium containing 3 to 30% by weight of at least one member selected from the group consisting of Nb, Ta, Cr, Mo, and Al are described. Several .alpha.-.beta. alloys are described along with a number of alloys containing Al, Mo, and Cr. No quaternary alloys of Ti, Nb, Ta, and Zr are described. The presence of Al, Cr, or Mo is undesirable because of their toxicity when the alloys are utilized in medical devices, such as surgical implants. The alloys of the present invention do not contain any Al, Cr, or Mo.
The alloys described in the two Wang et al patents contain an amount up to 3% of at least one eutectoid beta stabilizer selected from the group consisting of Fe, Mn, Cr, Co, and Ni, each of which is orders of magnitude more toxic than Ti, Zr, Nb, or Ta. The alloys described in these patents possess a modulus of elasticity (E) of 66.9 to 100 GPa with most of the alloys exhibiting a modulus of elasticity between 75 and 100 GPa. Unlike the alloys of Wang et al, the alloys of the present invention do not contain any of the toxic eutectoid stabilizers required by Wang et al.
Two specific alloys are described in Davidson et al 5,169,597; namely, a Ti--13Zr--13Nb and a Ti--18Zr--6Nb alloy. These alloys exhibit a modulus less than 85 GPa, and desirably between 60 and 85 GPa. The alloys of the present invention differ from those in Davidson et al, by having lower Ti and Zr contents and a content of Ta plus Nb which results in low moduli of elasticity.